Abstract

Background

Malaria parasites (Plasmodium sp.), including new species, have recently been discovered as low grade mixed infections
in three wild chimpanzees (Pan troglodytes schweinfurthii) sampled randomly in Kibale National Park, Uganda. This suggested a high prevalence
of malaria infection in this community. The clinical course of malaria in chimpanzees
and the species of the vectors that transmit their parasites are not known. The fact
that these apes display a specific behaviour in which they consume plant parts of
low nutritional value but that contain compounds with anti-malarial properties suggests
that the apes health might be affected by the parasite. The avoidance of the night-biting
anopheline mosquitoes is another potential behavioural adaptation that would lead
to a decrease in the number of infectious bites and consequently malaria.

Methods

Mosquitoes were collected over two years using suction-light traps and yeast-generated
CO2 traps at the nesting and the feeding sites of two chimpanzee communities in Kibale
National Park. The species of the female Anopheles caught were then determined and the presence of Plasmodium was sought in these insects by PCR amplification.

Results

The mosquito catches yielded a total of 309 female Anopheles specimens, the only known vectors of malaria parasites of mammalians. These specimens
belonged to 10 species, of which Anopheles implexus, Anopheles vinckei and Anopheles demeilloni dominated. Sensitive DNA amplification techniques failed to detect any Plasmodium-positive Anopheles specimens. Humidity and trap height influenced the Anopheles capture success, and there was a negative correlation between nest numbers and mosquito
abundance. The anopheline mosquitoes were also less diverse and numerous in sites
where chimpanzees were nesting as compared to those where they were feeding.

Conclusions

These observations suggest that the sites where chimpanzees build their nests every
night might be selected, at least in part, in order to minimize contact with anopheline
mosquitoes, which might lead to a reduced risk in acquiring malaria infections.